1. Field of the Invention
The present invention relates to meteorological techniques for estimating a precipitation rate by means of radar.
2. Description of the Related Art
When estimating the rate of rainfall from radar measurements, one is generally confronted with the problem of attenuation of the radar wave, and with the problem of the natural variability of rain.
The concept of coherent radar with polarization diversity associated with a so-called ZPHI algorithm is described in WO 99/38028 as a solution for those two obstacles under operational conditions.
ZPHI is a profiler algorithm which basically uses as input a measured reflectivity profile Za and a constraint given by a differential phase difference ΦDP between two points r1 and r2 on a line of sight.
On the basis of those measurements, the specific attenuation A and a parameter known as N0* are determined, which parameter quantifies the distribution of raindrop sizes.
The rainfall rate R to be estimated is obtained as a function of those two parameters for two reasons. First, the specific attenuation A is not subject to attenuation effects. Using it to estimate R thus enables the attenuation problem to be overcome. Second, the parameter N0* suffices to describe the natural variability of rain.
The ZPHI algorithm is equally applicable in the X and C bands, which frequency bands are sensitive to attenuation.